Thanks for all the advice. I recently bought the boat and have been doing the engine maintenance. One item was the anodes. I do not think they had been serviced in over 5 years. I removed the one on the head and installed anode (the original was totally gone). I tried to get one off the block but ended up rounding off the anode plug- looks like I will have to drill it out without damaging the block threads. I have not had a chance to try to remove the 2nd anode in block. I have heard maybe holding dry ice to the plug then put a wrench to it. I did use a laser cut socket on the plug and it still rounded- I think there is major corrosion between plug and block.